Dear Mr/Ms ：
Today I'm writing to you to ask for a five-day leave, for I've got cold last night with carlessness.
This morning my mother took me to see the doctor,who told me to stay in bed for some days. So I am very sorry to be absent from school, especially your interesting lessons. I'll be sure to make up for the missed lessons after I recover from the illness.
Yours ever,
.
Dear Mr.,
I'm sorry to tell you that I caught a cold and I'm not feeling well now.I am adviced to stay in bed for two days and can't go to school then.But I think I'll get well soon and be back the day after tomorrow.
Yours sincerely,
20xx年月日
Dear teacher,
I am not feel very well this days,and cough Seriously,so,I went to see a doctor yesterday, the doctor told me that I have had a badly cold, he let me stay in bed day and night, taking pills three times a day.As you know, I can not go to scholl.Cared by my families,I am sure I will get well soon,I will try my best to catch up with my classmates. Thanks!
Yours,
Jack